Method and apparatus for additive manufacturing with powder material

ABSTRACT

A system for building a three dimensional green compact comprising a printing station configured to print a mask pattern on a building surface, wherein the mask pattern is formed of solidifiable material; a powder delivery station configured to apply a layer of powder material on the mask pattern; a die compaction station for compacting the layer formed by the powder material and the mask pattern; and a stage configured to repeatedly advance a building tray to each of the printing station, the powder delivery station and the die compaction station to build a plurality of layers that together form the three dimensional green compact.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/340,130, filed on Jun. 7, 2021, which is a continuation of U.S.patent application Ser. No. 16/381,042 filed on Apr. 11, 2019, now U.S.Pat. No. 11,059,100, which is a continuation of U.S. patent applicationSer. No. 16/092,770 filed on Oct. 11, 2018, now U.S. Pat. No.10,730,109, which is a National Phase of PCT Patent Application No.PCT/IL2017/050439 having International Filing Date of Apr. 9, 2017,which claims the benefit of priority under 35 USC § 119(e) of U.S.Provisional Patent Application No. 62/320,655 filed on Apr. 11, 2016 andU.S. Provisional Patent Application No. 62/473,605 filed on Mar. 20,2017.

The contents of the above applications are all incorporated by referenceas if fully set forth herein in their entirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to threedimensional (3D) printing with layers of powdered material and, moreparticularly, but not exclusively, to 3D printing of metal objects withpowdered metal as the building material.

A number of different processes for fabricating solid objects by 3Dprinting with successive layers of powdered material are known. Someknown 3D printing techniques selectively apply a liquid binder materialbased on a 3D model of the object, binding the material together layerby layer to create a solid structure. In some processes, the object isheated and/or sintered to further strengthen bonding of the material atthe end of the building process.

Selective Laser Sintering (SLS) uses a laser as the power source tosinter layers of powdered material. The laser is controlled to aim atpoints in space defined by a 3D model, binding the material togetherlayer by layer to create a solid structure. Selective laser melting(SLM) is comparable technique that applies full melting of the materialinstead of sintering. SLM is typically applied when the meltingtemperature of the powder is uniform, e.g. when pure metal powders areused as the building material.

U.S. Pat. No. 4,247,508 entitled “MOLDING PROCESS”, the contents ofwhich are incorporated herein by reference, describes a molding processfor forming a 3D article in layers. In one embodiment, planar layers ofmaterial are sequentially deposited. In each layer, prior to thedeposition of the next layer, a portion of its area is solidified todefine that portion of the article in that layer. Selectivesolidification of each layer may be accomplished by using heat and aselected mask or by using a controlled heat scanning process. Instead ofusing a laser to selectively fuse each layer, a separate mask for eachlayer and a heat source may be employed. The mask is placed over itsassociated layer and a heat source located above the mask. Heat passingthrough the opening of the mask will fuse together the particles exposedthrough the opening of the mask. The particles not exposed to the directheat will not be fused.

U.S. Pat. No. 5,076,869 entitled “MULTIPLE MATERIAL SYSTEMS FORSELECTIVE BEAM SINTERING”, the contents of which are incorporated hereinby reference, describes a method and apparatus for selectively sinteringa layer of powder to produce a part comprising a plurality of sinteredlayers. The apparatus includes a computer controlling a laser to directthe laser energy onto the powder to produce a sintered mass. For eachcross-section, the aim of the laser beam is scanned over a layer ofpowder and the beam is switched on to sinter only the powder within theboundaries of the cross-section. Powder is applied and successive layerssintered until a completed part is formed. Preferably, the powdercomprises a plurality of materials having different dissociation orbonding temperatures. The powder preferably comprises blended or coatedmaterials.

International Patent Publication No. WO2015/170330 entitled “METHOD ANDAPPARATUS FOR 3D PRINTING BY SELECTIVE SINTERING”, the contents of whichare incorporated herein by reference, discloses a method for forming anobject by 3D printing that includes providing a layer of powder on abuilding tray, performing die compaction on the layer, sintering thelayer that is die compacted by selective laser sintering or selectivelaser melting and repeating the providing, the die compaction and thesintering per layer until the three dimensional object is completed. Theselective sintering disclosed is by a mask pattern that defines anegative of a portion of the layer to be sintered.

SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present disclosurethere is provided a system and method for 3D printing with powderlayers. The system and method may be applied for forming a metal objectwith powdered metal as the building material. Optionally, other powderedmaterials such as plastics and ceramics may be used. According to someexemplary embodiments, a mask for each layer is first printed with athree dimensional printer that deposits solidifiable material, e.g. aphotopolymer material or a phase-change ink (e.g., thermal ink) and thena layer is formed by spreading a powder layer over the mask. Typicallythe mask traces a pattern of solidifiable material. The object beingformed from a plurality of layers is defined by the mask pattern thatoutlines a contour of the object with the solidifiable material andseparates the object from the surrounding area, e.g. the support area.

In some exemplary embodiments, the printed metal object (also referredto as the “green body”) is formed within a green compact (also referredto as a “green block”) and is subsequently sintered in a furnace at theend of the layer building process. In some embodiments, the solidifiablematerial forming the mask pattern is burnt, liquefied or evaporatedduring a dedicated heating process prior to sintering, and the object isextracted from the green compact by removing the surrounding supportingregions (also referred to as support or supporting areas or sections).According to some exemplary embodiments, the mask pattern applied perlayer provides dividing walls formed from the solidifiable material thatdivide the supporting regions surrounding the object into sections thatmay be easily separated from the object at the termination of the layerbuilding process.

According to an aspect of the present invention there is provided asystem for building a three dimensional green compact comprising: aprinting station configured to print a mask pattern on a buildingsurface, wherein the mask pattern is formed with a solidifiablematerial; a powder delivery station configured to apply a layer ofpowder material on the mask pattern; a die compaction station forcompacting the layer of powder material and the mask pattern; and astage configured to repeatedly advance a building tray to each of theprinting station, the powder delivery station and the die compactionstation to build a plurality of layers that together form the threedimensional green compact.

Optionally, the three dimensional green compact includes an object beingformed and a support region.

Optionally, the solidifiable material is selected from the groupconsisting of a phase-change ink, a thermal ink, a photopolymermaterial, wax, or any combination thereof.

Optionally, the phase-change ink is a configured to substantiallyevaporate at a temperature of above 300° C.

Optionally, the powder material is an aluminum alloy.

Optionally, the powder delivery station comprises a powder dispensingstation and a powder spreading station.

Optionally, the powder delivery station comprises: a powder hopperconfigured to store the powder material; a dispensing tip configured todispense the powder material; a powder dispensing tray configured toreceive the powder material from the dispensing tip; and an actuatorconfigured to deliver the powder material on the powder dispensing trayto the building tray.

Optionally, the powder dispensing tray includes a plurality of troughsconfigured to receive the powder material.

Optionally, the system includes a first rail configured to advance thepowder dispensing tray so that the hopper dispenses powder to each ofthe plurality of troughs of the powder dispensing tray.

Optionally, the actuator is configured to simultaneously flip theplurality of troughs.

Optionally, the actuator is configured to simultaneously open alongitudinal aperture located at the bottom of each of the plurality oftroughs.

Optionally, the system includes a second rail configured to advance thepowder dispensing tray so that the hopper dispenses powder along atrough on the powder dispensing tray.

Optionally, the hopper includes an auger through which the powdermaterial is controllably advanced into the dispensing tip.

Optionally, the powder delivery station includes a roller and whereinthe roller is actuated to both rotate and move across the layer forspreading the powder material.

Optionally, the roller is a forward roller.

Optionally, the powder delivery station includes a plurality of guttersconfigured to receive excess powder material falling from the edges ofthe building tray during roller movement across the layer for spreadingthe powder material.

Optionally, the plurality of gutters includes a first pair of guttersthat are actuated to move together with the roller during the spreadingof the powder material.

Optionally, the first pair of gutters is located below the lateral endsof the roller.

Optionally, each of the gutters of the first pair of gutters has alength of at least twice the diameter of the roller and is extending onboth sides of the roller lateral ends.

Optionally, the powder accumulated in said first pair of gutters iscontinuously removed from the gutter internal space during the spreadingof the powder material via an air suction.

Optionally, the plurality of gutters includes a second pair of gutterspositioned at a front end and back end of the building tray with respectto a direction of movement of the roller across the building tray.

Optionally, the second pair of gutters is actuated to move toward andaway from the building tray.

Optionally, the second pair of gutters is located at the level of theroller and an air suction is applied to remove the powder accumulated insaid gutters.

Optionally, the air suction is applied in the second pair of gutterswhen the air suction applied in the first pair of gutters is switchedoff.

Optionally, the powder delivery station is configured to recirculate theexcess powder material to the powder hopper.

Optionally, the powder delivery station includes at least one cycloneseparator configured to remove air from the powder material collectedfrom the plurality of gutters.

Optionally, the powder delivery station includes a plurality of cycloneseparators operated in series.

Optionally, the at least one cyclone separator includes a cap configuredto seal an outlet during operation of the cyclone separator.

Optionally, the powder delivery station includes a mesh configured toseparate the powder material from debris prior to delivering the powdermaterial to the powder hopper.

Optionally, the die compaction station includes side walls that areconfigured to be introduced around the building tray.

Optionally, the side walls are configured to be introduced around thebuilding tray based on contact of the layer with the compacting station.

According to an aspect of the present invention there is provided asystem for forming a three dimensional object comprising: a system forbuilding a three dimensional green compact as described above; and apost-processing station selected from the group consisting of a secondcompacting station, a heating station, a sintering station, and anycombination thereof.

According to an aspect of the present invention there is provided amethod for building a three dimensional green compact comprising:printing a mask pattern on a building surface with solidifiablematerial; forming a layer by spreading powder material on the maskpattern; compacting the layer; and repeating the printing, forming andcompacting until the three dimensional green compact is completed.

Optionally, the three dimensional green compact includes an object beingformed and a supporting region.

Optionally, spreading powder material comprises dispensing a pluralityof rows of powder material on the building surface and spreading theplurality of rows of powder material with a roller.

Optionally, the plurality of rows of powder material is preparedoff-line prior to dispensing on the building tray.

Optionally, the plurality of rows of powder material is positionedperpendicular to a spreading direction.

Optionally, the spreading includes rolling a roller over the powdermaterial.

Optionally, the spreading direction is inverted from one powder layer tothe subsequent one.

Optionally, the positioning of the plurality of rows of powder variesfrom one powder layer to the subsequent one.

Optionally, the method includes collecting excess powder material fromthe building surface based on the spreading and recirculating the excesspowder material to a powder hopper.

Optionally, the collecting and the recirculating are performed online.

Optionally, the method includes suctioning the excess powder to at leastone cyclone separator and separating the powder from air in the at leastone cyclone separator.

Optionally, the method includes operating a plurality of cycloneseparators in series.

Optionally, the method includes filtering the powder material from theat least one cyclone separator with a mesh and delivering powdermaterial filtered through the mesh to a powder hopper, wherein thepowder hopper provides the powder material for building the threedimensional green compact.

Optionally, the method includes applying heat during the compacting.

Optionally, the compacting is die compaction.

Optionally, the mask pattern includes a contour of the green compact perlayer.

Optionally, the printing, forming and compacting are performed inambient temperatures.

Optionally, a first layer is formed on a building tray coated with atacky material.

According to an aspect of the present invention there is provided amethod for forming a three dimensional object comprising: building athree dimensional green compact according to the method described above,wherein said three dimensional green compact comprises an object and asupport region including solidifiable material; and post-processing thegreen compact by removing the solidifiable material; separating theobject from the support region; and sintering the object.

Optionally, removing the solidifiable material and separating the objectfrom the support region is performed before sintering.

Optionally, removing the solidifiable material is performed duringsintering.

Optionally, post-processing further comprises compacting the greencompact as a whole.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 is a simplified schematic drawing of an exemplary 3D printingsystem in accordance with some embodiments of the present invention;

FIG. 2 is a simplified block diagram of an exemplary printer forprinting layers of masks for defining the object accordance with someembodiments of the present invention;

FIGS. 3A and 3B are simplified schematic representations of two types ofmask layer patterns printed on a building tray in accordance with someembodiments of the present invention;

FIG. 4 is a simplified block diagram of a powder dispensing station inaccordance with some embodiments of the present invention;

FIG. 5 is a simplified block diagram of a powder spreading station inaccordance with some embodiments of the present invention;

FIG. 6 is a simplified schematic cross sectional view of a green compactlayer including a printed mask pattern and a powder material inaccordance with some embodiments of the present invention;

FIGS. 7A and 7B are simplified schematic drawings of an exemplarycompacting system in a released and compressed state respectively inaccordance with some embodiments of the present invention;

FIGS. 8A and 8B are simplified schematic drawings of an exemplaryanti-peeling mechanism for a compacting system in a compacting state anda post compacting state respectively in accordance with some embodimentsof the present invention;

FIG. 9 is a simplified schematic representation of a layer after processcompaction and before milling in accordance with some embodiments of thepresent invention;

FIG. 10 is a simplified schematic representation of three printed layersfor forming an object in accordance with some embodiments of the presentinvention;

FIG. 11 is a simplified flow chart of an exemplary method forconstructing layers of a green compact by 3D printing in accordance withsome embodiments of the present invention;

FIG. 12 is a simplified flow chart of an exemplary method for forming anobject based on 3D printing in accordance with some embodiments of thepresent invention;

FIG. 13 is a simplified schematic drawing of an example per layerbuilding process in accordance with some embodiments of the presentinvention;

FIG. 14 is a simplified block diagram of an example building process inaccordance with some embodiments of the present invention;

FIG. 15 is an image of an example printing system in accordance withsome embodiments of the present invention;

FIG. 16 is an example drawing of a powder dispenser in accordance withsome embodiments of the present invention;

FIG. 17 is an example drawing of a roller, building tray and surroundinggutters in accordance with some embodiments of the present invention;and

FIG. 18 is an example drawing of a powder recirculation system inaccordance with some embodiments of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to threedimensional (3D) printing with layers of powdered material and, moreparticularly, but not exclusively, to 3D printing of metal objects withpowdered metal as the building material.

As used herein, the term “solidifiable material” refers to material thatis a liquid or can be liquefied to allow depositing and can besolidified when deposited on a building surface. An example ofsolidifiable material is a solidifiable ink, which is liquid whenprinted on a building surface and can be solidified on it. Nonlimitative examples of solidifiable inks include, photocurable polymers(also referred to as “photopolymer material”), thermal inks (alsoreferred to as “phase-change inks”) an example of which is wax, and anycombination thereof. Thermal ink and phase change ink as used herein areinterchangeable terms and may be defined as a material that is solid atroom temperature (e.g. about 25° C.) has a melting point of less than120° C., viscosity of less than 50 cPs between the melting pointtemperature and 120° C. and that evaporates with substantially no carbontraces at a temperature of above 100° C. Substantially, no carbon tracesis defined as less than wt. 5% or less than wt. 1%. In some exampleembodiments, the thermal ink has a melt temperature of between 55-65° C.and a working temperature of about 65-75° C., the viscosity may bebetween 15-17 cPs. According to embodiments of the present invention,the thermal ink is configured to evaporate in response to heating withlittle or no carbon traces.

As used herein, the terms “green compact” and “green block”interchangeably refer to a block formed by the successive compaction oflayers formed by spreading powder material over a mask of solidifiablematerial. A green compact typically includes in its volume one or moreobjects being built, also referred to as “green body(ies)”, a supportingregion surrounding the green body, and solidifiable material. Thesolidifiable material defines the contour of the green body and may beused to divide the supporting region into sub-regions that are moreeasily removed. When referring to a specific layer of the green compact,the green body appears as a “model area” (or “object area”) and thesupporting region appears as one or more “supporting area(s)”.

As used herein, the terms “mask” and “mask pattern” interchangeablyrefer to a structure formed by the deposition of a solidifiable materialonto a building surface (e.g. building tray, preceding layer). The maskpattern generally includes one or more solid structural elements such aslines, points, corners, perimeters, or any other geometric structurethat results from the solidification of the solidifiable material. Thesolidifiable material may solidify either spontaneously or afteractivation of an external trigger, e.g. UV light.

As used herein, the term “printing station” or “3D printing station”includes any apparatus suitable to deposit one or more solidifiablematerials on a building surface. The printing station may include aprinthead, an extruder, and/or any other suitable means known in theart.

According to some embodiments of the present invention, there isprovided a 3D printing system and method for building an object forsintering using a mask pattern formed with at least one solidifiablematerial such as a phase-change ink, a thermal ink, a photopolymermaterial, wax or any combination thereof. Optionally, the thermal inkhas low carbon content and is configured to evaporate in response toheating leaving little or no carbon traces. In some exemplaryembodiments, the system and method is applied to building objects withpure metals such as aluminum. It is noted that the system and method isnot limited for use with pure aluminum and can also be used for buildingwith metal alloys, plastics, ceramics and/or a combination of differentmaterials.

According to some embodiments of the present invention, the systemincludes a building tray, a 3D printer for printing a mask pattern, apowder dispenser with spreader for applying powdered material over themask, a first compaction unit for compacting the layers and optionally amilling (or grinding) unit for shaving off the upper surface of each alayer. According to some exemplary embodiments, a controlled lineardrive may repeatedly advance the building tray to each of the 3D printer(also referred to as “digital printing station” or “printing station”),powder dispensing station and powder spreading station (that arecombined in some embodiments into a “powder delivery station”) and thecompacting station (also referred to as “process compaction station”),for building the plurality of layers. Optionally, the building tray iscoated with a tacky material such as glue prior to building the firstlayer.

In some exemplary embodiments, the system additionally includes a secondcompacting station, and a furnace sintering station for compacting andthen sintering the multiple layers at the termination of the layerbuilding process, respectively. In some embodiments, the mask burnsduring a first stage in the sintering process (in specific conditionsand gas environment) and then the multiple layers are merged. In someother example embodiments, the mask is formed from thermal ink and thethermal ink is configured to evaporate as opposed to burn in a dedicatedheating process prior to sintering or during sintering. After thededicated heating process or after the sintering, the object isseparated from the surrounding material.

According to some exemplary embodiments, a powder dispenser spreads aplurality of rows of powder material per layer. In some exampleembodiments, the rows are positioned on the building tray so that theyare parallel with the spreader, e.g. parallel with an axis of rotationof the spreader and perpendicular to linear movement of the rolleracross the building tray. Optionally, 2-20 rows of powder are spread perlayer. In some example embodiments, the rows are spread off-line over aspreading tray comprising a plurality of troughs and then transferred tothe building tray (for example by opening or flipping simultaneously theplurality of troughs). Dispensing a plurality of rows over the buildingtray may be configured to help the spreader spread the powder moreevenly over the building tray and may also maintain a constant heightfor the layer across the building tray. The spreader is typically aroller with a defined diameter that is actuated to rotate while movingacross the building tray to spread the powder. During spreading, excesspowder may be collected in gutters positioned around the building tray.

According to some example embodiments, the powder collected in thegutters is mixed into a container, e.g. a hopper including a supply ofpowder for building the subsequent layers. Suction may be applied tocollect the material in the gutters and advance the material through apowder recirculation system. In some example embodiments, an excessamount of powder is dispensed per layer on the building tray tofacilitate spreading an even layer of powder. Optionally, the amount ofpowder that is dispensed is 2 to 5 times more than the amount used perlayer. During spreading, a relatively large portion of the powder thatis dispensed per layer is pushed into the gutters and circulated backinto the hopper. Optionally, the recirculated powder is actively mixedinto the powder supply in the hopper.

In some example embodiments, gutters are positioned on each of the foursides of the building tray. In some example embodiments, the front andback gutters (in relation to movement direction of the roller) have asmall range of motion that allow them to move toward the building trayto collect the powder and move away from the building tray to allow thebuilding tray to move in the vertical direction and lateral directionand advance to the next station. Optionally, between 50%-80% of thepowder that is dispensed is collected in the gutters and recycled. Thepowder recirculation system facilitates a more efficient use of thepowder and avoids unnecessary accumulation of powder.

In some example embodiments, the powder recirculation system includesgutters to collect the excess powder, a vacuum pump to transport theexcess powder, one or more cyclone separators to gather powder from theair, a mesh to separate any debris from the gathered powder and avibrator to facilitate filtering through the mesh. In some examples, thepowder recirculation system includes a series of cyclone separators.Optionally, the series facilitates collecting powder particles withdifferent sizes and weights at a high efficiency, e.g. fornon-homogenous powders. In some example embodiments, the outlet at thebottom of each of the cyclone separators is sealed during operation ofthe cyclone separator. Optionally, the seal is released on all thecyclone separators once the separation activity is complete and thepowder is then dispensed on a mesh that filters the powder from anydebris or clumped powder that may have been collected. Optionally, themesh is actuated by a vibrator. The powder filtered through the mesh maythen be introduced into the hopper and mixed into the powder in thehopper.

According to some exemplary embodiments, the 3D printer is an inkjet 3Dprinter, e.g. a PolyJet™ printer provided by Stratasys Ltd., Israel. Inspecific embodiments, the mask pattern printed by the 3D printer tracesa perimeter of each layer pattern and optionally also includes radiallines that extend from points along the perimeter toward edges of thebuilding tray. The radial lines of ink material may facilitateseparating the object within the traced perimeter of the layer patternsfrom the building material outside the perimeter of the masks that isnot part of the object. During the layer building process, buildingmaterial may serve as support for building negative slope surfaces ofthe object or hollow volumes included in the object. In some exemplaryembodiments, the 3D printer includes inkjet printing heads assembled ona scanning printing block that moves over the building tray to scan thelayer during printing, while the building tray remains stationary.Alternatively, a precision stage may be used to advance the buildingtray in the scanning direction while the inkjet printing head blockremains stationary in that direction, and movable in the orthogonaldirection or completely stationary. In some embodiments, the entire maskpattern of the specific layer may be printed in a single pass.

In some exemplary embodiments, the compaction unit is a die compactionunit including walls that surround the building tray and the layer ofpowder spread on it and maintains the footprint of the layers. In anexample, the footprint of the tray may be between 20×20 cm to 25×25 cm.Optionally, the compaction unit includes a hydraulic press and operatesin room temperature. The hydraulic press may press each layer with up to300 MPa of pressure, e.g. in a case of the use of al6061 Aluminumpowder. In most cases, the compaction pressure per layer may be lowerthan 300 MPa, e.g. less than 100 MPa. The density (measured in gr/cm³)of the powder is typically lower than the density of the wroughtmaterial as the powder volume contains air. The quality of thecompaction can be measured by the relative density, defined by thecompacted powder density divided by the wrought material density (in %).The spreading pressure exerted by the roller may increase the density ofa layer from about 50% to 60%, and the per layer compaction pressure mayincrease the density of a layer to about 70-90%. Optionally an averagelayer thickness prior to compaction may be between 100-300 μm.

During compaction the solidifiable material forming the mask pattern,may be subject to deformation near the upper surface of the layer. Amilling (or grinding) unit optionally provides for removing the portionof the layer that may be subject to deformation. Optionally, 10%-50% ofthe layer is removed by the milling (or grinding) unit. Optionally,20-50 μm of the layer is removed. Optionally, a thickness of the layeris defined so that after compaction and optional milling (or grinding),the layer will have a desired pre-defined thickness. An additional maskmay then be printed on the existing layer after the milling (orgrinding) to continue the layer building process. According to someexemplary embodiments, the entire layer building process may beperformed at ambient temperature. The ability to operate at ambienttemperature is typically associated with lower cost of operation andalso reduced cost of the system. Operation at high temperaturestypically requires more safety measures that are typically associatedwith higher costs.

According to some exemplary embodiments, the ensemble of layers formingthe green compact may be compacted again in a second compacting stationat higher pressure and temperature and also for a longer duration, afterthe layer building process is complete. Alternatively, the secondcompacting station is not required.

Building with aluminum is known to be advantageous due to its lightweight, heat and electricity conduction, and its relative resistance tocorrosion. Typically, the melting temperature of aluminum is relativelylow. One of the challenges of building with aluminum powder is that thealuminum particles of the powder tend to form an aluminum oxide coating,e.g. alumina. The aluminum oxide coating introduces a barrier betweenthe aluminum particles that interferes with bonding of the particlesduring sintering. The final result is typically an object with reducedstrength due to poor bonding between the powdered elements.

In some exemplary embodiments, the compaction strength applied in thecompaction process is defined to provide permanent deformation of thepowder layer, e.g. press the powder particles past its elastic state andinto its plastic state. Typically, the density and thereby themechanical strength of the object is improved by compaction. Thecompaction also promotes bonding during sintering by breaking up thealumina layer to expose the aluminum and allow direct engagement betweenaluminum particles of the powdered material. Optionally, compactionincreases thermal conductivity of the powder layer and allows for moreuniform sintering. Optionally, compaction improves the bonding betweenlayers and prevents layer separation that may occur after sintering. Insome example embodiments, the compaction per layer results in a greencompact in the form of a block that includes one or more green bodies(i.e., objects being formed) optionally separated by a solidifiablematerial deposited by the 3D printer such as solid phase-change ink orphotopolymer material (i.e. the mask pattern).

In some exemplary embodiments, the second compacting station compactsthe ensemble at 150-350 MPa pressure at a temperature of up to 430° C.for between 1-6 minutes. Optionally, this second compacting station isalso a die compaction station that maintains the Z-axis accuracy.Although the defined object is only within perimeters of the maskpattern, the additional powder material forming the rectangular layersis maintained and used to support the shape of the object during the diecompaction. Optionally, it is the second compacting station thatfinalizes the compaction of the green compact.

Furnace sintering is typically applied after a final compaction stagebut may also be applied directly after the final layer of the greencompact has been produced. Temperatures and duration of sinteringtypically depend on the powder material used and optionally on the sizeof the object. In some exemplary embodiments, the powder material isaluminum. The first stage of the furnace sintering process may be at 300to 400° C. for a period of 20 to 180 minutes. The furnace environmentcan be inert (Nitrogen) or aerated at this stage. In some embodiments,where the solidifiable material forming the mask includes a photopolymermaterial, a first stage during the sintering process may be configuredto burn the photopolymer material. The polymer is burned using itsstructural oxygen molecules and does not need external oxygen supply.Sintering at higher temperatures may typically be performed in anitrogen environment. Optionally, the object may be at 570° C. to 630°C. for 60 to 180 minutes, for Aluminum powder. For stainless steelpowder, for instance, the temperature may reach 1250° C. Optionally, thefurnace is capable of changing temperature at a rate of 2-20° C./min.Typically, sintering is performed over a plurality of stages, each stageat a defined temperature and for a defined period. Optionally, the blockis cooled after the first stage, and the object is extracted andsintering completed.

In some example embodiments, the 3D printing system described hereinprovides for printing at improved speed. For example, printing time perlayer may be between 25-35 seconds and an estimated building time forthe green body, i.e. object being printed, including about 400 layersmay be for example 4 hours. A block that is a green compact that isbuilt on the building tray may include a plurality of embedded greenbodies, e.g. 1-15 objects. An example footprint of the block may be20×20 cm.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the Examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways.

Referring now to the drawings, FIG. 1 shows a simplified block diagramof an exemplary 3D printing system in accordance with some embodimentsof the present invention. According to some embodiments of the presentinvention, a 3D printing system 100 is integrated on a working platform500. According to some embodiments of the present invention, workingplatform 500 includes a precision stage 250 on which a building tray 200is advanced through a plurality of stations for printing a green compact15 one layer at a time. Typically, precision stage 250 is a linearstage, e.g. an X-Z stage providing motion along a single axis, e.g. an Xaxis while building a layer and also providing motion in the verticaldirection (Z-axis) for adjusting height of tray 200, e.g. lowering tray200 as each new layer is added.

According to some embodiments of the present invention, working platform500 includes a printing platform station 30, for printing a maskpattern, a powder dispensing station 10 for dispensing a powder layer ontray 200, a powder spreading station 20 for spreading a layer ofdispensed powder on the printed mask pattern, a compacting station 40for compacting the layer of powder, and a milling station 50 for shavingupper surface of a current layer prior to printing another layer.Typically for each layer, printing tray 200 advances to each of thestations and then repeats the process until all the layers have beenprinted. In some exemplary embodiments, tray 200 is advanced in onedirection with a stop at printing platform station 30 and then reversesdirection with stops at powder dispensing station 10, powder spreadingstation 20, compacting station 40 and milling station 50. According tosome embodiments of the present invention, a controller 300 controlsoperation of 3D printing system 100 and coordinates operation of each ofthe stations with positioning and/or movement of tray 200 on precisionstage 250. Typically, controller 300 includes and/or is associated withmemory and processing ability.

According to some exemplary embodiments, at the end of the layerbuilding process, green compact 15 may be advanced or positioned in asecond compacting station 60 for final compaction and then to sinteringstation 70 for sintering. Alternatively, the first compacting station 40completes the compaction during the layer building process or at the endof the layer building process. In some specific embodiments, during thesintering process, the mask built by printing station 30 burns and thegreen compact 15 solidifies. The mask burning allows green compact 15defined within the layer wise perimeters of the mask to be separatedfrom the portion of the layers outside the perimeters.

Optionally, inert gas source 510 is source of nitrogen. Typically,sintering station 70 and optionally second compacting station 60 arestand alone stations that are separate from working platform 500.Optionally, green compact 15 is manually positioned into sinteringstation 70 and optionally second compacting station 60 and not byprecision stage 250.

Optionally, each of second compacting station 60 and sintering station70 have a separate controller for operating the respective station.

Reference is now made to FIG. 2 showing a simplified schematic drawingof an exemplary 3D printing system in accordance with some embodimentsof the present invention. According to some embodiments of the presentinvention, printing platform station 30 includes a direct inkjetprinting head 35 that deposits photopolymer material 32 based on agenerated mask data 39. Typically, the mask pattern is defined by maskdata 39 that is typically stored in memory. Typically, the mask data isgenerated by a computer aided design (CAD) software program or the like.

In some exemplary embodiments, printing head 35 is stationary andprinter controller 37 together with system controller 300 control timingfor depositing material 32 as tray 200 advances under printing head 35.Typically a curing unit 33 cures the deposited material as tray 200advances under printing head 35. Optionally, printing head 35 and curingunit 33 are mounted on a Y axis stage and move in a directionperpendicular to tray 200. Alternatively, tray 200 is stationary duringprinting and printing head 35 and curing unit 33 are supported by an X,Y or XY stage for moving printing head 35 in one or more directions.Typically, printing head 35 includes an array of nozzles through whichmaterial is selectively deposited.

Reference is now made to FIG. 3A showing a simplified schematicrepresentation of one mask layer pattern printed on a building tray inaccordance with some embodiments of the present invention. According tosome embodiments of the present invention, printing head 35 prints acontour 150 of the object being formed at each layer with a solidifiablematerial, such as photopolymer material or phase-change ink. Typically,the mask first layer is printed on building tray 200 or other buildingsurface. In some exemplary embodiments, printing head additionallyprints rays 155 extending from contour 150 toward edges of building tray200 or toward gutters 255 at edges of building tray 200. In someexemplary embodiments, rays 155 introduce cuts in the powder outside ofcontour 150 so that that area outside contour 150 (i.e. the supportingarea) can be easily separated from the object within the contour areaafter the building layers are solidified at the end of the buildingprocess. Typically, unmasked/unpatterned portions are filled with thepowder material that is used to construct the object.

Referring now to FIG. 3B, in some exemplary embodiments, solidifiablematerial may be patterned to fully or partially occupy supporting areas157 as opposed to rays 155 outside contour 150 to fill portions of thelayer that are not to become part of the object. Optionally, supportingareas are formed by a combination of solidifiable material structuresand powder material.

In some exemplary embodiments, the volume of powder material used toform the layers may be conserved by printing a portion of the areaoutside contour 150 with solidifiable material. In some exemplaryembodiments, the amount of solidifiable material printed outside contour150 depends on the type of support that the solidifiable materialprovides around the object.

Reference is now made to FIG. 4 showing a simplified block diagram of apowder dispensing station in accordance with some embodiments of thepresent invention. Typically, powder dispensing station 10 includes acontainer 12 storing powder 51, an auger 14 for extracting a definedquantity and/or volume of powder 51 through a tube 16 and onto tray 200.In some exemplary embodiments, the defined volume is adjusted over thecourse of the building process based on feedback from system 100 and/orcontroller 300. Optionally, powder 51 is dispensed while tray 200 is inmotion so that powder 51 is spread over a length of tray 200. In someexemplary embodiments, powder dispensing station 10 is adapted todeliver powder aluminum. In other exemplary embodiments, other metals,alloys and/or materials are stored and delivered by powder dispensingstation 10. Optionally, container 12 includes a plurality of componentsthat are mixed. Optionally, container 12 includes a mechanism for mixingcontents stored.

Reference is now made to FIG. 5 showing a simplified block diagram of apowder spreading station in accordance with some embodiments of thepresent invention. Typically, spreading station 20 includes a motorizedroller 25 rotatably mounted on an axle 24. In some exemplaryembodiments, a linear motor 22 engages axle 24 and moves across thelayer for spreading an even layer of powder. In some exemplaryembodiments, a height of table 200 is adjusted, e.g. moved up/down witha Z stage in order to obtain a defined layer thickness. In someexemplary embodiments, a powder layer of about 150 μm thick, e.g. 100 μmto 300 μm thick is spread with roller 25. Typically, the powder layer isspread over the mask layer and has a height above the mask layer priorto compaction. Typically, after compaction, the height of the powderlayer is reduced to the height of the mask layer. In some exemplaryembodiments, a thickness of a layer after compaction is monitored and aheight of tray 200 is adjusted to alter a thickness of a current layerto compensate for drifts or variations in layer thicknesses of one ormore previous layers. Optionally, a mechanism of powder recirculation isconnected to container 12 for collecting the non-spread powder andreturning it back to container 12.

In some exemplary embodiments, roller 25 extends substantially over anentire length of tray 200 and only one pass of the roller is required tospread the powder.

Optionally, roller 25 is operated while tray 200 is in motion.Optionally, roller 25 is held at a height above tray 200 and is loweredwith a Z elevator as required for spreading.

Reference is now made to FIG. 6 showing a simplified schematic crosssectional view of a green compact layer including a printed mask patternand powder material in accordance with some embodiments of the presentinvention. According to some embodiments of the present invention, alayer 300 is formed by first printing a mask pattern 150 and thenspreading powder 51 over the mask pattern. Layer 300 is typicallydefined so that powder 51 reaches same height as a height of mask 150.

In some example embodiments, a layer of glue or other tacky material isspread on tray 200 prior to building over tray 200, e.g. prior toprinting the first mask 150. The layer of glue may be a 1-10 μm thick.In some example embodiments the thin layer of glue stabilizes the layerson the tray and also provides for separating the layers from thebuilding tray at the termination of the layer building process. In someexample embodiments, the thickness of the glue layer as well as itsmechanical properties are selected to facilitate piercing of the powderthrough the glue layer. The piercing may help stabilize the firstlayer(s) on the building tray.

Reference is now made to FIGS. 7A and 7B showing simplified schematicdrawings of an exemplary die compaction station shown in a released andcompressed state respectively in accordance with some embodiments of thepresent invention.

According to some embodiments of the present invention, a layer 300 iscompacted after spreading the powder layer over the mask layer.According to some embodiments of the present invention, as thecompaction process it performed per layer, the compaction stationgenerates a die per layer.

According to some embodiments of the present invention, the compactionstation includes a piston 42 that is operative to provide the compactionpressure for compacting a layer 300. According to some embodiments ofthe present invention, during compaction, piston 42 is raised through abore 49 and optionally pushes rod 42A in working platform 500 orprecision stage 250 and lifts building tray 200 towards surface 45positioned above tray 200. Optionally, the addition of rod 42A reducesthe distance that piston 42 is required to move to achieve thecompaction.

Optionally, once layer 300 makes contact with surface 45 walls 43 closein around the layer 300 to maintain a constant footprint of the layer300 during compaction.

In some exemplary embodiments, tray 200 is secured to one or more linearguides 41 that ride along linear bearings 46 as piston 42 elevatesand/or lowers tray 200.

Optionally, tray 200 is lifted against one or more compression springs47. In some exemplary embodiments, gravitational force as well assprings 47 provide for lowering piston 42 after compacting layer 300.

According to some embodiments of the present invention, a pressure of upto 250 MPa or 300 MPa is applied to compact a powder and mask layer.Typically, the applied pressure provides for removing air and bringingpowder in layer 300 past its elastic state so that permanent deformationof the layer is achieved. Optionally, the compaction provides forincreasing the relative density of the layer to about 70% to 75%. Forseveral alloys the relative density may reach up to 90%. Optionally,compaction reduces the thickness of a layer by up to 25%. Optionally, acompaction pressure of around 50-90 MPa is applied. Optionally, thecompaction is performed at room temperature.

In some exemplary embodiments, upper surface 45 is heated, e.g.pre-heated with a heating element 44 during compaction and warm diecompaction is performed. When heating surface 45, layer 300 can reachits plastic and/or permanent deformation state with less pressureapplied on the layer. Optionally, in aluminum powder case, upper surface45 is heated to a temperature of 150° C., e.g. 150°-200° C. Typicallythere is a tradeoff between compaction temperature and pressure.Increasing the temperature during compaction may provide for reachingplastic deformation at lower pressure. On the other hand, reducingtemperature of upper surface 45 may reduce the energy efficiency of thecompaction since higher pressure may be required.

Typically, the pressure and temperature applied is defined based on thepowder material and the thickness of layer 300.

In some exemplary embodiments, e.g. when aluminum powder is used, thecompaction is operative to break up the oxide layer, e.g. the alumina onthe powdered particles. Typically, exposing the aluminum promotes directengagement between aluminum particles of the powdered material andimproves bonding of the particles during sintering.

In some exemplary embodiments, mask pattern 150 may deform duringcompaction. Typically, deformation will occur near surface 45 where themask pattern 150 is exposed. Powder 51 held by walls 43 surrounding thelayer typically provide support for mask pattern 150 below the uppersurface so that no deformation occurs below the upper surface of thelayer.

According to some embodiments of the present invention, the height ofthe object, e.g. height of one or more layers of the object as it isbeing built, is detected, determined and/or sensed at the compactionstation. Optionally, a height of tray 200 while pressed against surface45 is detected. According to some embodiments of the present invention,controller 300 (FIG. 1 ) monitors the height and/or the change in heightand provides input to powder dispensing station and/or Z stage of tray200 when adjustments in layer thicknesses are required to compensate fora drift from a desired height and/or change in height. In some exemplaryembodiments, controller 300 uses one or more lookup tables stored inmemory or mathematical formula to control adjustments in layerthicknesses.

In some exemplary embodiments, one or more stations along a path ofprecision stage 250 are supported on rails extending along the pathand/or by one or more bridges, e.g. bridge positioned over workingplatform 500. In some exemplary embodiments, compacting station 40includes a piston 42 positioned below working platform 500 that isoperated to raise tray 200 with rod 42A toward a flattening surface 45positioned above tray 200 or other surface as is described in furtherdetail herein below.

Reference is now made to FIGS. 8A and 8B showing a simplified schematicdrawings of an exemplary anti-peeling mechanism for a compacting systemshown in a compacting state and a post compacting state respectivelyboth in accordance with some embodiments of the present invention.According to some embodiments of the present invention, a foil and/orfilm 149 is attached to the sides of 45 loosely. During compaction, foil149 pressed between surface of 45 and layer 300. At the end of thecompaction process, building tray 200 moves down, and the layer isseparated gently from the foil, and avoiding layer peeling) ispositioned between layer 300 and contact surface 45 of die 48 duringcompaction. Optionally, the foil has a thickness between 0.1-0.4 mm,e.g. 0.3 mm. Optionally, the foil is a stainless steel 302; 301 or 316Lfoil. Typically, foil 149 protects surface 45 from accumulating powderand also prevents substantial peeling of layer 300 during separation ofsurface 45. The present inventor has found that this gradual detachmentof the foil avoids peeling and/or loss of material from layer 300 onfoil 149.

Reference is now made to FIG. 9 showing a simplified schematicrepresentation of a layer after process compaction and before milling(or grinding) in accordance with some embodiments of the presentinvention. According to some exemplary embodiments, an upper portion 301of layer 300 may include deformation in the mask 150 due to thecompaction. According to some exemplary embodiments, layer 300 is milled(or grinded) to remove the upper surface 301 including the deformation.The portion that is removed is schematically indicated by line 410. Alayer may have a thickness of about 50-180 μm after process compactionand prior to milling (or grinding). Milling (or grinding) may shave offbetween 10-50 μm of layer 300. In some exemplary embodiments, layer 300may be defined to have a thickness of about 25-120 μm after processcompaction and milling.

Reference is now made to FIG. 10 showing a simplified schematicrepresentation of three printed layers for forming an object inaccordance with some embodiments of the present invention. According tosome embodiments of the present invention, mask pattern 150 maytypically form a continuous boundary or contour with one mask pattern150 touching another mask pattern as additional layers 300 are added.This continuous boundary formed from stacked mask patterns 150 defines a3D contour of the object being formed and sections within the supportingareas outside of the object at the end of the green compact formingprocess.

Reference is now made to FIG. 11 is a simplified flow chart of anexemplary method for constructing an object by 3D printing in accordancewith some embodiments of the present invention. According to someembodiments of the present invention, the method includes printing amask pattern per layer that defines a boundary of an object or greenbody being formed and also extensions that later facilitate separatingthe object from surrounding material (block 305). After printing themask, the method further includes dispensing powder layer on a buildingtray (block 310) and spreading the powder layer over the mask pattern toobtain a uniform layer of powder (block 320). In some exemplaryembodiments, the powder is aluminum. Optionally, other metals oralternatively ceramic material is used as the building material, e.g.the powder. Optionally, the powder is a mix of a plurality of materials.In some exemplary embodiments, each layer is compacted (block 330) andthen the upper surface of the compacted layer is optionally milled(block 340) to remove any deformations formed on the upper surface inthe mask due to compaction. Typically, the compaction provides forremoving air from the printed layer.

Optionally, the compaction also provides for breaking an oxidationcoating that typically forms on particles of the metal powder, e.g.aluminum powder. Typically, these steps are repeated until all thelayers have been printed.

According to some exemplary embodiments, the layer building processes asdescribed in FIG. 11 may be performed on an automated stage and inambient temperatures. Due to the ambient temperature conditions, thereis no requirement to provide a positive flow of inert gas or to addadditional precautions that may typically be needed when working at hightemperatures or inert gas environment. Typically, providing a positiveflow of inert gas or adding precautions against combustion is associatedwith increased cost. Possible advantages of the layer building processas described herein include safer operation and lower cost.

Reference is now made to FIG. 12 showing a simplified flow chart of anexemplary method for forming an object based on 3D printing inaccordance with some embodiments of the present invention. According tosome exemplary embodiments, once the building layer process is complete,the built layers forming a green compact are removed from the automatedstage (block 405) and compacted again at optionally a higher pressure,temperature and/or longer duration (block 410). In some exemplaryembodiments, the final compaction of the whole green body is performedat a pressure of between 150-300 MPa, in aluminum case e.g. 250 MPa or atemperature below 430° C. Optionally, the layers are compacted for anextended duration of time, e.g. 2-6 minutes. Typically, the compactionis die compaction so that only the Z-axis is compacted during theprocess. After compaction, sintering is typically applied (block 415).In some exemplary embodiments, sintering is applied in a plurality ofstages. Optionally at a first stage, the built layers are heated atrelatively low temperature, e.g. below 400° C. over a first duration,e.g. 20-180 minutes. In case of the use of aluminum powder and someother metals like stainless steel, this step may require an inertenvironment of Nitrogen. In some embodiments, the mask pattern is burnedat this stage, mainly due to the oxygen contained in the polymer. At asecond stage the temperature may be raised, e.g. 450° C. and thistemperature may be maintained for a second duration, e.g. 0-30 minutes.Rising and cooling may be at defined rate, e.g. 10° C./min. At a thirdstage, the temperature may be raised again, e.g. 570-630° C. (in case ofaluminum powder, depending on the alloy in use) and this temperature maybe maintained for a third duration, e.g. 60-120 minutes. In case ofaluminum powder—all these steps may be processed in an inertenvironment. After sintering and cooling, the object may be extractedfrom the block of layers. Other post processing steps (i.e. stepsperformed after the building of the green compact) may be necessary toimprove the density of the printed objet.

An aspect of some exemplary embodiments of the present inventionprovides for a system for building a three dimensional objectcomprising: a digital printing station configured to print a mask on abuilding surface, wherein the mask is formed from at least one ofphotopolymer material and wax material that is configured to burn duringsintering; a powder delivery station configured to apply a layer ofpowder material on the mask pattern; a process compaction station forcompacting per layer of powder material, wherein the compaction stationincludes a die for receiving the layer; a stage configured to repeatedlyadvancing the building tray to each of the digital printing station, thepowder delivery station and the process compaction station to build aplurality of layers that together form the three dimensional object; anda sintering station configured to sinter the plurality of layers.

Optionally, the process compacting station includes a heating elementfor warming a surface of the die that interfaces with the layer.

Optionally, the process compacting station is operable to apply up to300 MPa of pressure on the layer.

Optionally, the process compacting station includes side walls that areconfigured to be introduced around the building tray based on contact ofthe layer with the compacting station. The side walls are locked inplace such that they have minimal movement, e.g. less than 0.1 mm underthe reaction forces developed in the powder block while compacting.

Optionally, wherein the process compacting station includes ananti-peeling mechanism, the anti-peeling mechanism including a foilpositioned between the die.

Optionally, the system includes a milling or grinding station, whereinthe milling or grinding station is configured to remove a surface of thelayer after compaction, wherein the stage is configured to repeatedlyadvance the building tray to each of the digital printing station, thepowder delivery station, the process compaction station and the millingor grinding station to build a plurality of layers that together formthe three dimensional object.

Optionally, the milling or grinding station is configured to shave off10-40% of the layer thickness.

Optionally, the system includes a final compaction station configured tocompact the plurality of layers.

Optionally, the final compaction station heat compacts the plurality oflayers over a plurality of heating stages.

Optionally, the powder delivery station includes a motorized roller thatis configured to move across the layer for spreading the powder.

Optionally, the powder delivery station includes a gutter for receivingexcess powder based on the roller moving across the layer for spreadingthe powder.

Optionally, the powder delivery station is configured to recycle theexcess powder.

An aspect of some exemplary embodiments of the present inventionprovides for a method for building a three dimensional objectcomprising: printing a mask on a building surface, wherein the mask isformed from at least one of a photopolymer material and wax that isconfigured to burn during sintering; spreading a layer of powder on themask pattern; compacting the layer of powder; repeating the printing,spreading and compacting until layers of the three dimensional object iscompleted; and sintering the layers of the three dimensional object.

Optionally, the method includes applying heat during the compacting.

Optionally, the compacting is die compaction.

Optionally, the mask includes a contour of the object per layer.

Optionally, the mask additionally includes a pattern that extends fromthe contour of the object per layer toward edges of a footprint of thelayer.

Optionally, the method includes milling or grinding the layer aftercompaction and before printing an additional mask on the layer.

Optionally, 10-40% of the layer thickness is removed based on themilling or grinding.

Optionally, the printing, spreading and compacting are performed inambient temperatures.

Optionally, the method includes performing a final heat compaction priorto sintering, wherein the final heat compaction is performed over aplurality of heating stages.

Optionally, the method includes burning at least one of the photopolymermaterial and the wax during the sintering.

Reference is now made to FIG. 13 showing a simplified schematic drawingof another exemplary per layer building process in accordance with someembodiments of the present invention. FIG. 13 shows an example thirdlayer 506 in the process of being built over an example first layer 502and second layer 504. In some exemplary embodiments, a mask pattern 510is dispensed per layer with a three dimensional printer. According tosome exemplary embodiments, mask pattern 510 is formed from asolidifiable material such as phase-change ink. Mask pattern 510 mayphysically contact a mask pattern 510 in a previous layer, e.g. layer504 or may be patterned over an area of the previous layer including thebuilding material. A height of mask pattern 510 per layer may besubstantially the same as a height of the layer or may optionally beshorter than a height of the layer, e.g. portion 510A of mask pattern510 in layer 504. Optionally, milling is not required.

According to some examples, powder 51 is spread over the mask pattern510 and across a footprint of a building tray 200. In some exampleembodiments, powder 51 is spread with a roller 25. Optionally, roller 25is actuated to both rotate about its axle 24 and to move across buildingtray 200 along an X axis. Once powder 51 is spread across the footprintof tray 200, compaction 520 may be applied on the entire layer tocompact layer 506. Typically, a height of layer 506 is reduced due toprocess compaction.

Reference is now made to FIG. 14 showing a simplified block diagram ofan exemplary building process and to FIG. 15 showing a simplifiedschematic drawing of an exemplary 3D printing system in accordance withsome embodiments of the present invention. According to some exemplaryembodiments, an object (i.e. a green body) may be constructed layer bylayer within a green compact in a cyclic process. Each cycle of thecyclic process may include the steps of printing a mask pattern (block530) at a printing station 535, dispensing and spreading a powdermaterial (block 540) over the mask at a dispensing and spreading station545 (also referred to as “powder delivery station”) and compacting thepowder layer including the mask pattern (block 550) at a compactingstation 555. In some exemplary embodiments, the mask pattern is formedfrom a solidifiable material such as phase-change ink. In some exemplaryembodiments, the compaction is performed as described in reference toFIGS. 7A and 7B. According to embodiments of the present in invention,each cycle builds one layer of the green compact and the cycle isrepeated until all the layers have been built. Optionally, one or morelayers may not require a mask pattern and the step of printing the maskpattern (block 530) may be excluded from selected layers. Optionally,one or more layers may not require powder material and the step ofdispensing and spreading a powder material (block 540) may be excludedfrom selected layers.

According to embodiments of the present invention, this cyclic processyields a green compact or green block. The green compact may include oneor more objects (i.e. green bodies) surrounded by mask and buildingmaterial forming support regions outside of the object. According toembodiments of the present invention, both the object(s) and thesurrounding support regions including the mask make up a green compactformed with the powder material that was dispensed and spread during thecyclic process. According to embodiments of the present invention, themask pattern that was printed defines a boundary around the object(s)and optionally regions within the block that enables extracting theobject(s) from the surrounding material. According to some exampleembodiments, the object(s) once extracted from the surrounding materialmay be further post processed, e.g. may be further compacted over one ormore steps prior to sintering.

Reference is now made to FIG. 16 showing an example drawing of a powderdispenser in accordance with some embodiments of the present invention.According to some exemplary embodiments, a powder dispenser 600dispenses a plurality of rows of powder material per layer. In someexample embodiments, the rows of powder dispensed by powder dispenser600 are spread off-line on a dedicated spreading tray 670 including aplurality of troughs 660 in which powder 51 is received. In some exampleembodiments, powder dispenser 600 includes a first rail 610 thatadvances the troughs below the hopper 640 so that the hopper maydispense powder into each of the plurality of troughs 660 of the powderdispensing tray in turn, and a second rail 620 that moves the powderdispensing tray below the hopper such that the hopper 640 dispensespowder 51 through a dispensing tip 650 along each of the plurality oftroughs 660 until all the troughs have been filled. Typically, movementalong each of first rail 610 and second rail 620 is actuated with adedicated motor. In some example embodiments, powder hopper 640 includesan auger for precise powder dosing per row, e.g. per trough 660.Typically, the auger is controllably rotated with a dedicated motor.Optionally, the auger is actuated while second rail 620 moves the powderdispensing tray under powder hopper 640 as it dispenses powder 51 alongeach of the plurality of troughs 660 and is not actuated while firstrail 610 moves the powder dispensing tray such that powder hopper 640 isabove each of the plurality of troughs 660 in turn.

According to some exemplary embodiments, powder dispenser 600 includes apiston 630 that actuates transferring the rows of powder material fromspreading tray 670 to the building tray 200 (FIG. 15 ) once all the rowshave been prepared. In some example embodiments, piston 630 isconfigured to simultaneously flip each of the troughs 660 of spreadingtray 670 onto building tray 200. In other example embodiments, each ofthe troughs 660 includes a longitudinal aperture along the base of thetrough that is covered or closed and piston 630 is configured to actuatesimultaneously opening the longitudinal apertures to dispense rows ofpowder material onto building tray 200.

According to some example embodiments, the rows are positioned on thebuilding tray so that they are parallel with a roller 25 (FIG. 13 ),e.g. parallel with axle 24 of rotation of roller 25 and perpendicular tolinear movement of roller 25 across the building tray, e.g.perpendicular to the X axis (FIG. 13 ). Optionally, 2-20 rows of powderare spread on spreading tray 670 per layer. According to some exemplaryembodiments, roller 25 spreads the rows of powder 51 across buildingtray 200.

Reference is now made to FIG. 17 showing an exemplary spreading unit inaccordance with some embodiments of the present invention. According tosome exemplary embodiments, a spreading unit 700 includes a roller 25, apair of side gutters 730 and a pair of end gutters 740. Side gutters 730and end gutters 740 are configured to collect excess powder 51 onbuilding tray 200 as roller 25 is rolled across building tray 200.According to some exemplary embodiments, roller 25 is actuated to movealong a rail 710 across building tray 200 along the X axis (FIG. 13 )and is also actuated with a motor 720 to rotate about its axle 24.Typically, motor 720 travels on rail 710 and rotates roller 25 as itmoves across building tray 200 along a direction of the X axis. Roller25 may be actuated to move forward, backwards along a direction of the Xaxis or both forward and backwards along a direction of the X axis.Optionally, spreading unit 700 alternates between moving roller 25 in aforward and backward direction. Typically, a direction of rotation ofroller 25 about its axle 24 is adapted to the linear direction ofmovement of roller 25.

According to some exemplary embodiments, each of side gutters 730 ispositioned below each end of roller 25 and the pair of side gutters 730move together with roller 25 along rail 710. Side gutters are configuredto collect excess powder 51 that falls off of building tray 200 asroller 25 spreads powder 51. In some example embodiments, a length ofside gutter 730 along a direction of rail 710 (in a direction of the Xaxis) is at least twice a diameter of the roller 25.

According to some exemplary embodiments, each of end gutters 740 islocated near an edge of building tray 200 that is parallel to roller 25and perpendicular to rail 710 and extends at least along the entire edgeof building tray 200 to collect excess powder that falls off buildingtray 200 as roller 25 spreads powder 51. In some example embodiments,end gutters 740 are positioned at the level at which roller 25 touchesbuilding tray 200 or building surface, e.g. top of uppermost layer. Endgutters 740 move together with roller 25 along rail 710 but are alsoseparately actuated to move toward and away from building tray 200 asneeded. Optionally, movement of end gutters 740 toward and away from thebuilding tray 200 is in the order of magnitude of 1 mm to 1 cm. In someexample embodiments, end gutters are configured to move toward buildingtray 200 to collect the excess powder and to move away from the buildingtray during movement of the building tray, e.g. vertical or lateralmovement of building tray 200.

According to some example embodiments, a vacuum (creating an airsuction) is applied to remove the powder accumulated in each of the sidegutters 730 and end gutters 740 as the roller spreads powder 51 acrossbuilding tray 200. Optionally, the vacuum is alternately applied to sidegutters 730 and end gutters 740 based on position of roller 25.Optionally, the vacuum is alternately applied to each of the pair of endgutters 740 based on position of roller 25. In some exemplaryembodiments, between 50%-80% of powder 51 that is dispensed per layer onbuilding tray 200 is collected in side gutters 730 and end gutters 740.The collected powder may be transferred to a recirculation system thatreintroduces the collected powder to powder hopper 640.

Reference is now made to FIG. 18 showing an example drawing of a powderrecirculation system in accordance with some embodiments of the presentinvention. According to some example embodiments, a powder recirculationsystem 800 includes a container 810 that is configured to receive powdercollected from side gutters 730 and end gutters 740 of spreading unit700, one or more cyclone separators 820 configured to remove air frompowder in container 810, a mesh 840 to separate debris from the powderseparated by cyclone separators 820 and a spout 860 through which thepowder is dispensed into powder hopper 640. In some exemplaryembodiments, cyclone separators 820 are operated in series. Optionally,the series facilitates collecting powder particles with different sizesand weights at a high efficiency by varying the filtering conditions(e.g. air flow speed, cyclone diameter) from one cyclone separator 820to another. For example, contents in container 810 may first beintroduced into one of cyclone separators 820. Air removed from thefirst cyclone separator may be introduced into a second one of cycloneseparators 820. Optionally, the air removed from the first cycloneseparator may still contain powder material and that material may beseparated in the second cyclone separator. This process may be continuedfor all the cyclone separators. Typically, powder is substantiallycontinuously introduced into container 810 during the spreading processand substantially continuously streamed from one cyclone separators tothe next so that all the cyclone separators are operated simultaneously.Optionally, powder recirculation system 800 includes four cycloneseparators.

According to some example embodiments, the cyclone separators includecaps configured to seal an outlet during operation of the cycloneseparator. In some example embodiments, the cap is periodically releasedto collect the powder from cyclone separators 820. Typically, the cap isreleased between periods of operation of spreading unit 700. Optionally,a piston 830 controls a simultaneous release of all the caps. In someexample embodiments, powder collected from cyclone separators 820 isfiltered through mesh 840 to separate it from any debris or clumpedpowder that may have been collected. Optionally, a piston 850 actuatesvibration of mesh 840 to facilitate the filtering. The powder filteredthrough the mesh may then be introduced into the hopper and mixed intothe powder in the hopper 640.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

It is the intent of the Applicant(s) that all publications, patents andpatent applications referred to in this specification are to beincorporated in their entirety by reference into the specification, asif each individual publication, patent or patent application wasspecifically and individually noted when referenced that it is to beincorporated herein by reference. In addition, citation oridentification of any reference in this application shall not beconstrued as an admission that such reference is available as prior artto the present invention. To the extent that section headings are used,they should not be construed as necessarily limiting. In addition, anypriority document(s) of this application is/are hereby incorporatedherein by reference in its/their entirety.

What is claimed is:
 1. A method for building a three dimensional greencompact comprising: printing a mask pattern on a building surface withsolidifiable material; forming a layer by spreading powder material onthe mask pattern; compacting the layer; and repeating the printing,forming and compacting until the three dimensional green compact iscompleted.
 2. The method according to claim 1, wherein the threedimensional green compact includes an object being formed and asupporting region.
 3. The method according to claim 1, wherein spreadingpowder material comprises dispensing a plurality of rows of powdermaterial on the building surface and spreading the plurality of rows ofpowder material with a roller.
 4. The method according to claim 3,wherein the plurality of rows of powder material is prepared off-lineprior to dispensing on the building tray.
 5. The method according toclaim 3, wherein the plurality of rows of powder material is positionedperpendicular to a spreading direction.
 6. The method according to claim1, wherein the spreading includes rolling a roller over the powdermaterial.
 7. The method according to claim 1, comprising inverting aspreading direction between subsequent powder layers.
 8. The methodaccording to claim 1, wherein the positioning of the plurality of rowsof powder varies from one powder layer to the subsequent one.
 9. Themethod according to claim 1, comprising collecting excess powdermaterial falling from the edges of the building surface during thespreading and recirculating the excess powder material to a powderhopper.
 10. The method according to claim 9, comprising suctioning theexcess powder to at least one cyclone separator and separating thepowder from air in the at least one cyclone separator.
 11. The methodaccording to claim 10, comprising operating a plurality of cycloneseparators in series.
 12. The method according to claim 10, comprisingfiltering the powder material from the at least one cyclone separatorwith a mesh and delivering powder material filtered through the mesh toa powder hopper, wherein the powder hopper provides the powder materialfor building the three dimensional green compact.
 13. The methodaccording to claim 1, comprising applying heat during the compacting.14. The method according to claim 1, wherein the compacting comprisesdie compaction.
 15. The method according to any one of claim 1, whereinthe mask pattern includes a contour of the green compact per layer. 16.The method according to claim 1, wherein the printing, the forming andthe compacting are performed in ambient temperatures.
 17. The methodaccording to claim 1, wherein a first layer is formed on a building traycoated with a tacky material.
 18. A method for forming a threedimensional object comprising: building a three dimensional greencompact according to the method of claim 1, wherein said threedimensional green compact comprises an object and a support regionincluding said solidifiable material; and separating the object from thesupport region.
 19. The method of claim 18, comprising sintering theobject.
 20. The method according to claim 19, wherein said separating isexecuted before sintering.